Pep-1 as a novel probe for the in situ detection of hyaluronan

Peptide-based self-assembled monolayers (SAMs): what peptides can do for SAMs and vice versa

Self-assembled monolayers (SAMs) represent highly ordered molecular materials with versatile biochemical features and multidisciplinary applications. Research on SAMs has made much progress since the early begginings of Au substrates and alkanethiols, and numerous examples of peptide-displaying SAMs can be found in the literature. Peptides, presenting increasing structural complexity, stimuli-responsiveness, and biological relevance, represent versatile functional components in SAMs-based platforms. This review examines the major findings and progress made on the use of peptide building blocks displayed as part of SAMs with specific functions, such as selective cell adhesion, migration and differentiation, biomolecular binding, advanced biosensing, molecular electronics, antimicrobial, osteointegrative and antifouling surfaces, among others. Peptide selection and design, functionalisation strategies, as well as structural and functional characteristics from selected examples are discussed. Additionally, advanced fabrication methods for dynamic peptide spatiotemporal presentation are presented, as well as a number of characterisation techniques. All together, these features and approaches enable the preparation and use of increasingly complex peptide-based SAMs to mimic and study biological processes, and provide convergent platforms for high throughput screening discovery and validation of promising therapeutics and technologies.

Multipotential Role of Growth Factor Mimetic Peptides for Osteochondral Tissue Engineering

Articular cartilage is characterized by a poor self-healing capacity due to its aneural and avascular nature. Once injured, it undergoes a series of catabolic processes which lead to its progressive degeneration and the onset of a severe chronic disease called osteoarthritis (OA). In OA, important alterations of the morpho-functional organization occur in the cartilage extracellular matrix, involving all the nearby tissues, including the subchondral bone. Osteochondral engineering, based on a perfect combination of cells, biomaterials and biomolecules, is becoming increasingly successful for the regeneration of injured cartilage and underlying subchondral bone tissue. To this end, recently, several peptides have been explored as active molecules and enrichment motifs for the functionalization of biomaterials due to their ability to be easily chemically synthesized, as well as their tunable physico-chemical features, low immunogenicity issues and functional group modeling properties. In addition, they have shown a good aptitude to penetrate into the tissue due to their small size and stability at room temperature. In particular, growth-factor-derived peptides can play multiple functions in bone and cartilage repair, exhibiting chondrogenic/osteogenic differentiation properties. Among the most studied peptides, great attention has been paid to transforming growth factor-β and bone morphogenetic protein mimetic peptides, cell-penetrating peptides, cell-binding peptides, self-assembling peptides and extracellular matrix-derived peptides. Moreover, recently, phage display technology is emerging as a powerful selection technique for obtaining functional peptides on a large scale and at a low cost. In particular, these peptides have demonstrated advantages such as high biocompatibility; the ability to be immobilized directly on chondro- and osteoinductive nanomaterials; and improving the cell attachment, differentiation, development and regeneration of osteochondral tissue. In this context, the aim of the present review was to go through the recent literature underlining the importance of studying novel functional motifs related to growth factor mimetic peptides that could be a useful tool in osteochondral repair strategies. Moreover, the review summarizes the current knowledge of the use of phage display peptides in osteochondral tissue regeneration.

Bacteriophage-based biomaterials for tissue regeneration

Bacteriophage, also called phage, is a human-safe bacteria-specific virus. It is a monodisperse biological nanostructure made of proteins (forming the outside surface) and nucleic acids (encased in the protein capsid). Among different types of phages, filamentous phages have received great attention in tissue regeneration research due to their unique nanofiber-like morphology. They can be produced in an error-free format, self-assemble into ordered scaffolds, display multiple signaling peptides site-specifically, and serve as a platform for identifying novel signaling or homing peptides. They can direct stem cell differentiation into specific cell types when they are organized into proper patterns or display suitable peptides. These unusual features have allowed scientists to employ them to regenerate a variety of tissues, including bone, nerves, cartilage, skin, and heart. This review will summarize the progress in the field of phage-based tissue regeneration and the future directions in this field.

Hyaluronan biology: A complex balancing act of structure, function, location and context

Cell-matrix interactions are fundamental to many developmental, homeostatic, immune and pathologic processes. Hyaluronan (HA), a critical component of the extracellular matrix (ECM) that regulates normal structural integrity and development, also regulates tissue responses during injury, repair, and regeneration. Though simple in its primary structure, HA regulates biological responses in a highly complex manner with balanced contributions from its molecular size and concentration, synthesis versus enzymatic and/or oxidative-nitrative fragmentation, interactions with key HA binding proteins and cell associated receptors, and its cell context-specific signaling. This review highlights the different, but inter-related factors that dictate the biological activity of HA and introduces the overarching themes that weave throughout this special issue of Matrix Biology on hyaluronan.

Chemical-induced contact allergy: from mechanistic understanding to risk prevention

Chemical allergens are small molecules able to form a sensitizing complex once they bound to proteins. One of the most frequent manifestations of chemical allergy is contact hypersensitivity, which can have serious impact on quality of life. Allergic contact dermatitis is a predominantly CD8 + T cell-mediated immune disease, resulting in erythema and eczema. Chemical allergy is of considerable importance to the toxicologist, who has the responsibility of identifying and characterizing the allergenic potential of chemicals, and estimating the risk they pose to human health. This review aimed at exploring the phenomena of chemical-induced contact allergy starting from a mechanistic understanding, immunoregulatory mechanisms, passing through the potency of contract allergen until the hazard identification, pointing out the in vitro models for assessing contact allergen-induced cell activation and the risk prevention.

Enhanced lubrication on tissue and biomaterial surfaces through peptide-mediated binding of hyaluronic acid

Lubrication is key for the efficient function of devices and tissues with moving surfaces, such as articulating joints, ocular surfaces and the lungs. Indeed, lubrication dysfunction leads to increased friction and degeneration of these systems. Here, we present a polymer-peptide surface coating platform to non-covalently bind hyaluronic acid (HA), a natural lubricant in the body. Tissue surfaces treated with the HA-binding system exhibited higher lubricity values, and in vivo were able to retain HA in the articular joint and to bind ocular tissue surfaces. Biomaterials-mediated strategies that locally bind and concentrate HA could provide physical and biological benefits when used to treat tissue-lubricating dysfunction and to coat medical devices.

Characterization of a novel recombinant hyaluronan binding protein for tissue hyaluronan detection

Tumor necrosis factor-Stimulated Gene 6 protein (TSG-6) is a hyaluronan (HA)-binding glycoprotein containing an HA-binding Link module. Because of its well-defined structure, HA binding properties and small size, TSG-6 is an excellent candidate as an alternative to animal-derived HA-binding protein (HABP) for the detection of HA. The present work describes the generation and characterization of a novel recombinant HA-binding probe obtained by fusion of a modified TSG-6 Link module with mutationally inactivated heparin-binding sequence and the Fc portion of human IgG1 (TSG-6-ΔHep-Fc) for tissue HA detection in histological samples. Direct binding assays indicated strong binding of TSG-6-ΔHep-Fc to HA, with little residual binding to heparin. Histolocalization of HA in formalin-fixed, paraffin-embedded tissue sections using biotin-TSG-6-ΔHep-Fc resulted in hyaluronidase-sensitive staining patterns similar to those obtained with biotin-HABP, but with improved sensitivity. HA was detected in many human tissues, and was most abundant in soft connective tissues such as the skin dermis and the stroma of various glands. Digital image analysis revealed a linear correlation between biotin-HABP and biotin-TSG-6-ΔHep-Fc staining intensity in a subset of normal and malignant human tissues. These results demonstrate that TSG-6-ΔHep-Fc is a sensitive and specific probe for the detection of HA by histological methods.

Hyaluronan digestion controls DC migration from the skin

The breakdown and release of hyaluronan (HA) from the extracellular matrix has been hypothesized to act as an endogenous signal of injury. To test this hypothesis, we generated mice that conditionally overexpressed human hyaluronidase 1 (HYAL1). Mice expressing HYAL1 in skin either during early development or by inducible transient expression exhibited extensive HA degradation, yet displayed no evidence of spontaneous inflammation. Further, HYAL1 expression activated migration and promoted loss of DCs from the skin. We subsequently determined that induction of HYAL1 expression prior to topical antigen application resulted in a lack of an antigenic response due to the depletion of DCs from the skin. In contrast, induction of HYAL1 expression concurrent with antigen exposure accelerated allergic sensitization. Administration of HA tetrasaccharides, before or simultaneously with antigen application, recapitulated phenotypes observed in HYAL1-expressing animals, suggesting that the generation of small HA fragments, rather than the loss of large HA molecules, promotes DC migration and subsequent modification of allergic responses. Furthermore, mice lacking TLR4 did not exhibit HA-associated phenotypes, indicating that TLR4 mediates these responses. This study provides direct evidence that HA breakdown controls the capacity of the skin to present antigen. These events may influence DC function in injury or disease and have potential to be exploited therapeutically for modification of allergic responses.

The SOD mimic MnTM-2-PyP(5+) reduces hyaluronan degradation-induced inflammation in mouse articular chondrocytes stimulated with Fe (II) plus ascorbate

In pathological conditions, oxidative burst generates hyaluronan (HA) fragmentation with a consequent increase in the number of small HA oligosaccharides. These fragments are able to stimulate an inflammatory response in different cell types by activating the CD44 and the toll-like receptors 4 (TLR-4) and 2 (TLR-2). The stimulation of CD44 and TLRs in turn activates the NF-kB which induces the production of several pro-inflammatory mediators that amplify and perpetuate inflammation. We aimed to study the antioxidant effect of the SOD mimic, synthetic manganese porphyrin, Mn(III) 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (MnTM-2-PyP(5+)) on preventing HA degradation in mouse articular chondrocytes stimulated with Fe (II) plus ascorbate. Fe (II) plus ascorbate stimulation induced oxidative burst confirmed by high levels of hydroxyl radical/peroxynitrite production, increased lipid peroxidation and HA degradation. HA fragments highly induced mRNA expression and the related protein production of CD44, TLR-4 and TLR-2, NF-kB activation and significantly up-regulated the inflammatory cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and other pro-inflammatory mediators, i.e. matrix metalloprotease 13 (MMP-13) and inducible nitric oxide synthase (iNOS). Treatment of cells with MnTM-2-PyP(5+)was able to attenuate oxidative burst, HA degradation and NF-kB activation, and markedly decreased mRNA expression of CD44, and TLRs and the related protein synthesis, as well as the levels of up-regulated inflammatory mediators. Adding a specific HA-blocking peptide (PEP-1) to cells significantly reduced all the inflammatory parameters up-regulated by Fe (II) plus ascorbate, and increased MnTM-2-PyP(5+) activity. These findings suggest that HA degradation plays a key role in the initial inflammatory response of cartilage and antioxidants and could be a useful tool to prevent the propagation of this mechanism.

Protein kinase a mediated anti-inflammatory effects exerted by adenosine treatment in mouse chondrocytes stimulated with IL-1β

Hyaluronan (HA) fragments produced by degradation of native highly polymerized HA during inflammation may exacerbate proinflammatory responses in different pathologies. In contrast, the nucleoside adenosine (ADO) interacting with cell surface adenosine receptors A(2A) R, A(2B) R, A(1,) and A(3) , acts as endogenous modulator of the inflammation. The engagement of high-affinity A(2A) R by ADO activates a pathway leading to increased cAMP production. Elevated levels of cAMP associate with the activation of protein kinase A (PKA) able to inhibit NF-kB, hence exerting anti-inflammatory activity. In this study the effect of ADO treatment in normal murine chondrocytes stimulated with interleukin-1beta (IL-1beta) was investigated. mRNA and related protein levels were measured for enzymes, receptors and pro-inflammatory cytokines TNF-alpha, IL-6 and Il-18. IL-1beta stimulation significantly up-regulated HA levels, its fragmentation, cAMP, PKA, cytokine levels, and activated NF-kB. ADO treatment increased cAMP and PKA levels, while reduced NF-kB activation and cytokine levels. HA inhibition by specific synthetic HA blocking peptide (Pep-1) reduced IL-1beta action but not ADO activity. While A(2A) R inhibition by specific small interference RNA (siRNA) increased inflammation and decreased cAMP and PKA levels. This study suggests that HA is partially responsible for the up-regulation of proinflammatory cytokines in chondrocytes and that endogenous/exogenous ADO may reduce inflammation via PKA.

Hyaluronic acid-binding scaffold for articular cartilage repair

Hyaluronic acid (HA) is an extracellular matrix molecule with multiple physical and biological functions found in many tissues, including cartilage. HA has been incorporated in a number of biomaterial and scaffold systems. However, HA in the material may be difficult to control if it is not chemically modified and chemical modification of HA may negatively impact biological function. In this study, we developed a poly(ethylene glycol) hydrogel with noncovalent HA-binding capabilities and evaluated its ability to support cartilage formation in vitro and in an articular defect model. Chondrogenic differentiation of mesenchymal stem cells encapsulated in the HA-interactive scaffolds containing various amounts of exogenous HA was evaluated. The HA-binding hydrogel without exogenous HA produced the best cartilage as determined by biochemical content (glysocaminoglycan and collagen), histology (Safranin O and type II collagen staining), and gene expression analysis for aggrecan, type I collagen, type II collagen, and sox-9. This HA-binding formulation was then translated to an osteochondral defect model in the rat knee. After 6 weeks, histological analysis demonstrated improved cartilage tissue production in defects treated with the HA-interactive hydrogel compared to noninteractive control scaffolds and untreated defects. In addition to the tissue repair in the defect space, the Safranin O staining in cartilage tissue surrounding the defect was greater in treatment groups where the HA-binding scaffold was applied. In sum, incorporation of a noncovalent HA-binding functionality into biomaterials provides an ability to interact with local or exogenous HA, which can then impact tissue remodeling and ultimately new tissue production.

Adenosine A2A receptor activation and hyaluronan fragment inhibition reduce inflammation in mouse articular chondrocytes stimulated with interleukin-1β

Small hyaluronan (HA) fragments produced from native HA during inflammation contribute greatly to cell injury in many pathologies. HA oligosaccharides increase proinflammatory cytokine levels by activating both CD44 and toll-like receptor (TLR)-4. Stimulation of CD44 and TLR-4 then activates nuclear factor-κB, which induces the production of proinflammatory cytokines. The adenosine 2A receptor (A(2A)R) is also involved in several inflammation pathologies, and the nucleoside adenosine acts as a potent endogenous inhibitor of inflammation in various tissues by interacting with this receptor. The aim of this study was to investigate the effects of an HA-blocking peptide that inhibits the proinflammatory action of HA oligosaccharides produced during inflammation, together with a specific A(2A)R agonist in a model of normal mouse articular chondrocytes stimulated with interleukin (IL)-1β. IL-1β stimulation significantly increased mRNA expression and the related protein production of TLR-4, TLR-2, CD44 and A(2A)R in articular chondrocytes. The induced nuclear factor-κB activation was also associated with increased levels of inflammatory cytokines, including tumor necrosis factor-α and IL-6, and other inflammatory mediators, such as matrix metalloprotease-13 and inducible nitric oxide synthase. Treatment of chondrocytes with the HA-blocking peptide Pep-1 and/or a specific A(2A)R agonist (CGS-21680) significantly reduced all of the inflammatory parameters upregulated by IL-1β. These results suggest that the inflammatory response may be reduced either by blocking oligosaccharides from HA degradation or by A(2A)R stimulation.

Cathelicidin antimicrobial peptides inhibit hyaluronan-induced cytokine release and modulate chronic allergic dermatitis

Antimicrobial peptides such as cathelicidins can modulate inflammation by interfering with TLR function. Small fragment hyaluronan (HA) is released following injury, and is an endogenous ligand for TLR4 as well as CD44. In this study, we examined the interactions of cathelicidin with HA. Cathelicidin inhibited HA induced MIP-2 release from mouse bone marrow derived macrophages in a CD44 dependent manner but did not inhibit MALP2-induced MIP-2 release. This inhibitory activity was more potent than that of a peptide inhibitor of HA binding (Pep-1) and independent of Gi protein coupled or EGF-R signaling, both targets of cathelicidin inhibited HA-induced MIP-2 release. In assay of cell binding to HA, cathelicidins also significantly inhibited this process, suggesting that this antimicrobial peptide can interfere in other membrane binding events mediated by HA. The significance of this inhibition was demonstrated in a skin inflammation model induced by repeated application of 2,4-dinitrofluorobenzene. This induced an increase in HA at the site of application and was partially CD44 dependent. Camp(-/-) mice lacking cathelicidin demonstrated a large increase in ear swelling, cell infiltration, and MIP-2 expression compared with wild type mice. These results suggest that cathelicidin has anti-inflammatory activity in skin that may be mediated in part by inhibition of HA-mediated processes.

Recognition of hyaluronan released in sterile injury involves a unique receptor complex dependent on Toll-like receptor 4, CD44, and MD-2

Inflammation under sterile conditions is not well understood despite its importance in trauma and autoimmune disease. To investigate this process we established mouse models of sterile injury and explored the role of hyaluronan in mediating inflammation following injury. The response of cultured monocytes to hyaluronan was different than the response to lipopolysaccharide (LPS) despite both being dependent on Toll-like receptor 4 (TLR4). Cultured cells exposed to hyaluronan showed a pattern of gene induction that mimics the response seen in mouse skin after sterile injury with an increase in molecules such as transforming growth factor-beta2 and matrix metalloproteinase-13. These factors were not induced by LPS despite the mutual dependence of both hyaluronan and LPS on TLR4. Explanation for the unique response to hyaluronan was provided by observations that a lack of TLR4 or CD44 in mice diminished the response to sterile injury, and together with MD-2, was required for responsiveness to hyaluronan in vitro. Thus, a unique complex of TLR4, MD-2, and CD44 recognizes hyaluronan. Immunoprecipitation experiments confirmed the physical association of TLR4 and CD44. Taken together, our results define a previously unknown mechanism for initiation of sterile inflammation that involves recognition of released hyaluronan fragments as an endogenous signal of tissue injury.

Tumor Microenvironment Modulates Hyaluronan Expression: The Lactate Effect

Hyaluronan (HA) synthesis is a tightly regulated process and is partly controlled by the microenvironment (e.g., lactate concentration). Experimental evidence has indicated that the melanoma cells that synthesize large amounts of HA exhibit enhanced tumor cell growth and increased metastatic capacity compared to those expressing smaller amounts. Because most studies have examined HA expression on melanoma cells in vitro, we compared the patterns of HA expression by B16-F1 and B16-F10 melanoma cells in vitro and in situ. Cell surface HA expression was assessed with the HA-binding peptide Pep-1. B16-F1 melanoma cells showed significantly higher levels of Pep-1 binding compared with B16-F10 cells in vitro. On the other hand, expression levels of HA were comparable between B16-F1 and B16-F10 melanoma cells in cryostat sections. These results show that B16-F1 cells express high levels of HA in vitro and in vivo, while B16-F10 cells express high concentrations of HA only in the context of skin tumors. Finally, B16-F10 melanoma cells, but not B16-F1 cells, expressed high concentrations of HA after stimulation with lactate. We propose that components of the tumor microenvironment (e.g., lactate) can induce melanoma cells to express HA and thus acquire an aggressive phenotype.